Chapter 7 Packet-Switching Networks. Chapter 7 Packet-Switching Networks. Packet Switching. Network Layer. Network Service

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1 Chapter 7 Packet-Switching etwork etwork Operation & Topology Datagram and Virtual Circuit Structure of a Packet Switch Routing in Packet etwork Shortet Path Routing etwork Chapter 7 Packet-Switching etwork Overview: etwork Service, Operation and Topology etwork Layer etwork Layer: the mot complex Require the coordinated action of multiple, geographically ditributed network element (witche & router) Mut be able to deal with very large cale Billion of uer (people & communicating device) Bigget Challenge Addreing: where hould information be directed to? Routing: what path hould be ued to get information there? Packet Switching t t etwork Tranfer of information a payload in data packet Packet undergo random delay & poible lo Different application impoe differing requirement on the tranfer of information etwork Service etwork ervice End ytem α Meage Tranport etwork Data link Phyical etwork Data link Phyical Segment etwork Data link Phyical Meage Tranport etwork Data link Phyical etwork ervice End ytem β etwork can offer a variety of ervice to tranport Connection-oriented ervice or connectionle ervice Bet-effort or delay/lo guarantee etwork Service v. Operation etwork Service Connectionle Datagram Tranfer Connection-Oriented Reliable and poibly contant bit rate tranfer Internal etwork Operation Connectionle IP Connection-Oriented Telephone connection Variou combination are poible Connection-oriented ervice over Connectionle operation Connectionle ervice over Connection-Oriented operation Context & requirement determine what make ene

2 The End-to-End Argument for Sytem Deign An end-to-end function i bet implemented at a higher level than at a lower level End-to-end ervice require all intermediate component to work properly Higher-level better poitioned to enure correct operation Example: tream tranfer ervice Etablihing an explicit connection for each tream acro network require all network element (E) to be aware of connection; All E have to be involved in reetablihment of connection in cae of network fault In connectionle network operation, E do not deal with each explicit connection and hence are much impler in deign etwork Layer Function Eential Routing: mechanim for determining the et of bet path for routing packet require the collaboration of network element Forwarding: tranfer of packet from E input to output Priority & Scheduling: determining order of packet tranmiion in each E Optional: congetion control, egmentation & reaembly, ecurity End-to-End Packet etwork Example: Campu etwork Packet network very different than telephone network Individual packet tream are highly burty Statitical multiplexing i ued to concentrate tream Uer demand can undergo dramatic change Peer-to-peer application timulated huge growth in traffic volume Internet tructure highly decentralized Path travered by packet can go through many network controlled by different organization o ingle entity reponible for end-to-end ervice Departmental Server To Internet or wide area network Backbone Only High-peed outgoing packet campu leave LA backbone through net router connect dept router Organization Server R Gateway R S R S S R R R Server have redundant connectivity to backbone Connecting to The Internet Service Provider Key Role of Routing Campu etwork Border router Autonomou ytem or domain LA Border router Internet ervice provider Interdomain level Intradomain level network adminitered by ingle organization How to get packet from here to there? Decentralized nature of Internet make routing a major challenge Interior gateway protocol (IGP) are ued to determine route within a domain Exterior gateway protocol (EGP) are ued to determine route acro domain Route mut be conitent & produce table flow Scalability required to accommodate growth Hierarchical tructure of IP addree eential to keeping ize of routing table manageable

3 Chapter 7 Packet-Switching etwork Datagram and Virtual Circuit The Switching Function Dynamic interconnection of input to output Enable dynamic haring of tranmiion reource Two fundamental approache: Connectionle Connection-Oriented: Call etup control, Connection control Backbone etwork Switch Acce etwork Packet Switching etwork Meage Switching Uer etwork Tranmiion line Packet witch Packet witching network Tranfer packet between uer Tranmiion line + packet witche (router) Origin in meage witching Two mode of operation: Connectionle Virtual Circuit Meage Source Meage Switche Meage Meage Detination Meage witching invented for telegraphy Entire meage multiplexed onto hared line, tored & forwarded Header for ource & detination addree Routing at meage witche Connectionle Long Meage v. Packet Mbit meage ource det BER=p= - BER= - How many bit need to be tranmitted to deliver meage? Approach : end Mbit meage Probability meage arrive correctly Approach : end -kbit packet Probability packet arrive correctly. P c = ( ) e = e / P c = ( ) e = e. 9 On average it take about On average it take about. tranmiion/hop tranmiion/hop Total # bit tranmitted Total # bit tranmitted Mbit. Mbit Packet Switching - Datagram Meage broken into maller unit (packet) Source & detination addree in packet header Connectionle, packet routed independently (datagram) Packet may arrive out of order Pipelining of packet acro network can reduce delay, increae throughput Lower delay that meage witching, uitable for interactive traffic Packet Packet Packet Packet Packet

4 Routing Table in Datagram etwork Example: Internet Routing Detination addre 78 8 Output port 7 Route determined by table lookup Routing deciion involve finding next hop in route to given detination Routing table ha an entry for each detination pecifying output port that lead to next hop Size of table become impractical for very large number of detination Internet protocol ue datagram packet witching acro network etwork are treated a data link Hot have two-part IP addre: etwork addre + Hot addre Router do table lookup on network addre Thi reduce ize of routing table In addition, network addree are aigned o that they can alo be aggregated Dicued a CIDR in Chapter 8 Packet Switching Virtual Circuit Packet Packet Virtual circuit Packet Packet Call et-up phae et up pointer in fixed path along network All packet for a connection follow the ame path Abbreviated header identifie connection on each link Packet queue for tranmiion Variable bit rate poible, negotiated during call et-up Delay variable, cannot be le than circuit witching Connection Setup Connect requet Connect confirm SW Connect requet Connect confirm SW SW n Connect requet Connect confirm Signaling meage propagate a route i elected Signaling meage identify connection and etup table in witche Typically a connection i identified by a local tag, Virtual Circuit Identifier (VCI) Each witch only need to know how to relate an incoming tag in one input to an outgoing tag in the correponding output Once table are etup, packet can flow along path Virtual Circuit Forwarding Table Input VCI Output port 8 Output VCI 7 7 Each input port of packet witch ha a forwarding table Lookup entry for VCI of incoming packet Determine output port (next hop) and inert VCI for next link Very high peed are poible Table can alo include priority or other information about how packet hould be treated Chapter 7 Packet-Switching etwork Datagram and Virtual Circuit Structure of a Packet Switch

5 Packet Switch: Interection where Traffic Flow Meet Generic Packet Switch Input contain multiplexed flow from acce mux & other packet witche Flow demultiplexed at input, routed and/or forwarded to output port Packet buffered, prioritized, and multiplexed on output line Input port Controller Data path Control path Interconnection fabric (a) Output port Unfolded View of Switch Ingre Line Card Header proceing Demultiplexing Routing in large witche Controller Routing in mall witche Signalling & reource allocation Interconnection Fabric Tranfer packet between line card Egre Line Card Scheduling & priority Multiplexing Line Card Shared Memory Packet Switch Tranceiver Tranceiver To phyical port Framer Framer etwork proceor Backplane tranceiver To witch fabric Folded View circuit board i ingre/egre line card Phyical proceing Data link proceing etwork header proceing Phyical acro fabric + framing To other line card Interconnection fabric Ingre Proceing Connection Control Queue Control Shared Memory Output Buffering Small witche can be built by reading/writing into hared memory Crobar Switche Input (a) Input buffering 8 Self-Routing Switche Input (b) Output buffering Input Output Output Output Large witche built from crobar & multitage pace witche Require centralized controller/cheduler (who end to whom when) Can buffer at input, output, or both (performance v complexity) 7 Stage Stage Stage Self-routing witche do not require controller Output port number determine route () lower port, () upper port, () lower port 7

6 Chapter 7 Packet-Switching etwork Routing in Packet etwork Deirable Routing Feature Rapid and accurate delivery of packet Adaptability to network topology change Adaptability to traffic load condition Capability to dicover network connectivity Capability to avoid loop Scalability (to larger network) Low overhead (meaging) cot Chooing a Route in Packet etwork Creating the Routing Table ode (witch or router) Three poible (loopfree) route from to : --, ---, --- Which one i bet? Ue ome routing metric: Min delay? Min # hop? Max bandwidth? Min cot? Max reliability? eed information on tate of link Link up/down; congeted; delay or other metric eed to ditribute link tate information uing a routing protocol What information i exchanged? How often? Exchange with neighbor; Broadcat or flood eed to compute route baed on information Single metric; multiple metric Single route; alternate route Routing Algorithm Requirement Reponivene to change Topology or bandwidth change, congetion Rapid convergence of router to conitent et of route Freedom from peritent loop Optimality Reource utilization, path length Robutne Continue working under high load, congetion, fault, equipment failure, incorrect implementation Simplicity Efficient oftware implementation, reaonable proceing load Centralized v Ditributed Routing Centralized Routing All route determined by a central node All tate information ent to central node Problem adapting to frequent topology change Doe not cale Ditributed Routing Route determined by router uing ditributed algorithm State information exchanged by router Adapt to topology and other change Better calability

7 Static v Dynamic Routing Static Routing Set up manually, do not change; require adminitration Work when traffic predictable & network i imple Ued to override ome route et by dynamic algorithm Ued to provide default router Dynamic Routing Adapt to change in network condition Automated Calculate route baed on received updated network tate information Routing in Virtual-Circuit Packet etwork A Hot C VCI 7 D 8 Switch or router Route determined during connection etup Table in witche implement forwarding that realize elected route B Routing Table in VC Packet etwork Routing Table in Datagram Packet etwork ode Incoming Outgoing ode VCI ode VCI A A A A ode Incoming Outgoing ode VCI ode VCI 7 7 ode Incoming Outgoing ode VCI ode VCI 7 B 8 B B B 8 7 ode Detination ext node ode Detination ext node ode Detination ext node ode Incoming Outgoing ode VCI ode VCI C C ode Incoming Outgoing ode VCI ode VCI Example: VCI from A to D From A & VCI & VCI & VCI & VCI D & VCI ode Incoming Outgoing ode VCI ode VCI D D ode Detination ext node ode Detination ext node ode Detination ext node on-hierarchical Addree and Routing Hierarchical Addree and Routing R R R R o relationhip between addree & routing proximity Routing table require entrie each Prefix indicate network where hot i attached Routing table require entrie each

8 Flat v Hierarchical Routing Flat Routing All router are peer Doe not cale Hierarchical Routing Partitioning: Domain, autonomou ytem, area... Some router part of routing backbone Some router only communicate within an area Efficient becaue it matche typical traffic flow pattern Scale Specialized Routing Flooding Ueful in tarting up network Ueful in propagating information to all node Deflection Routing Fixed, preet routing procedure o route ynthei Flooding Send a packet to all node in a network o routing table available eed to broadcat packet to all node (e.g. to propagate link tate information) Approach Send packet on all port except one from where it arrived Exponential growth in packet tranmiion Flooding i initiated from ode : Hop tranmiion Flooding i initiated from ode : Hop tranmiion Flooding i initiated from ode : Hop tranmiion

9 Limited Flooding Time-to-Live field in each packet limit number of hop to certain diameter Each witch add it ID before flooding; dicard repeat Source put equence number in each packet; witche record ource addre and equence number and dicard repeat Deflection Routing etwork node forward packet to preferred port If preferred port buy, deflect packet to another port Work well with regular topologie Manhattan treet network Rectangular array of node ode deignated (i,j) Row alternate a one-way treet Column alternate a one-way avenue Bufferle operation i poible Propoed for optical packet network All-optical buffering currently not viable Example: ode (,) (,),,,, buy,,,,,,,,,,,, Tunnel from lat column to firt column or vice vera,,,,,,,,,,,,,,,, Chapter 7 Packet-Switching etwork Shortet Path Routing Shortet Path Routing Many poible path connect any given ource to any given detination Routing involve the election of the path to be ued to accomplih a given tranfer Typically it i poible to attach a cot or ditance to a link connecting two node Routing can then be formulated a a hortet path problem

10 Routing Metric Mean for meauring deirability of a path Path Length = um of cot or ditance Poible metric Hop count: rough meaure of reource ued Reliability: link availability; BER Delay: um of delay along path; complex & dynamic Bandwidth: available capacity in a path Load: Link & router utilization along path Cot: $$$ Shortet Path Approache Ditance Vector Protocol eighbor exchange lit of ditance to detination Bet next-hop determined for each detination Bellman-Ford (ditributed) hortet path algorithm Link State Protocol Link tate information flooded to all router Router have complete topology information Shortet path (& hence next hop) calculated Dijktra (centralized) hortet path algorithm Ditance Vector Approach: Do you know the way to Joe? Ditance Vector Concept Joe 9 Joe 9 Joe 9 Joe Local Signpot Direction Ditance Routing Table For each detination lit: ext ode Ditance det next dit Table Synthei eighbor exchange table entrie Determine current bet next hop Inform neighbor Periodically After change Shortet Path to SJ Focu on how node find their hortet path to a given detination node, i.e. SJ D i i C ij D j j Joe If D i i the hortet ditance to SJ from i and if j i a neighbor on the hortet path, then D i = C ij + D j Search for the hortet path i only ha local info from neighbor D j' j' C ij' i C ij C ij D i j" j D j D j" Joe Pick current hortet path

11 How Ditance Vector Work Hop From SJ Hop From SJ Hop From SJ SJ end accurate info Joe Hop- node calculate current (next hop, dit), & Accurate info about SJ end to neighbor ripple acro network gradually until hortet path converge Bellman-Ford Algorithm Conider computation for one detination d Initialization Each node table ha row for detination d Ditance of node d to itelf i zero: D d = Ditance of other node j to d i infinite: D j =, for j d ext hop node n j = - to indicate not yet defined for j d Send Step Send new ditance vector to immediate neighbor acro local link Receive Step At node j, find the next hop that give the minimum ditance to d, Min j { C ij + D j } Replace old (n j, D j (d)) by new (n j *, D j *(d)) if new next node or ditance Go to end tep Bellman-Ford Algorithm Iteration Initial ode (-, ) ode (-, ) ode (-, ) ode (-, ) ode (-, ) ow conider parallel computation for all detination d Initialization Each node ha row for each detination d Ditance of node d to itelf i zero: D d (d)= Ditance of other node j to d i infinite: D j (d)=, for j d ext node n j = - ince not yet defined Send Step Send new ditance vector to immediate neighbor acro local link Receive Step For each detination d, find the next hop that give the minimum ditance to d, Min j { C ij + D j (d) } Replace old (n j, D i (d)) by new (n j *, D j *(d)) if new next node or ditance found Go to end tep Table node for det SJ Table node for det SJ Joe Iteration ode ode ode ode ode Iteration ode ode ode ode ode Initial (-, ) (-, ) (-, ) (-, ) (-, ) Initial (-, ) (-, ) (-, ) (-, ) (-, ) (-, ) (-, ) (,) (-, ) (,) (-, ) (-, ) (, ) (-, ) (,) (,) (,) (, ) (,) (,) D =D + n = D =D + n = D = D = Joe Joe

12 Iteration ode ode ode ode ode Iteration ode ode ode ode ode Initial (-, ) (-, ) (,) (,) (-, ) (-, ) (,) (,) (-, ) (, ) (, ) (, ) (-, ) (-, ) (,) (,) (-, ) (,) (,) (,) Initial (,) (,) (,) (,) (, ) (, ) (,) (,) (,) (,) Joe etwork diconnected; Loop created between node and Joe Iteration ode ode ode ode ode Iteration ode ode ode ode ode Initial (,) (,) (, ) (,) (,) Initial (,) (,) (, ) (,) (,) (,) (,) (, ) (,) (,) (,) (,) (, ) (,) (,) (,7) (,) (, ) (,) (,) (,7) (,) (, ) (,) (,) (,7) (,) (, 7) (,) (,) 7 ode could have choen a next node becaue of tie Joe 7 7 ode could have choen a next node becaue of tie Joe Iteration ode (,) (,7) (,7) (,9) 7 9 ode (,) (,) (,) (,) ode (, ) (, ) (, 7) (, 7) ode (,) (,) (,) (,) 7 ode (,) (,) (,) (,) ode could have choe a next node becaue of tie Joe Counting to Infinity Problem (a) (b) X Update Before break After break ode (,) (,) (,) (,) (,) (,7) (,7) ode (,) (,) (,) (,) (,) (,) (,8) ode believe bet path i through each other (Detination i node ) ode (, ) (,) (,) (,) (,) (,7) (,7)

13 Problem: Bad ew Travel Slowly Remedie Split Horizon Do not report route to a detination to the neighbor from which route wa learned Poioned Revere Report route to a detination to the neighbor from which route wa learned, but with infinite ditance Break erroneou direct loop immediately Doe not work on ome indirect loop Split Horizon with Poion Revere (a) (b) Update Before break After break X ode ode (, ) (, ) (, ) (, ) (, ) (-, ) (-, ) (-, ) ode (, ) (-, ) (-, ) (-, ) ode believe bet path i through each other ode advertize it route to to node a having ditance infinity; node find there i no route to ode advertize it route to to node a having ditance infinity; node find there i no route to ode find there i no route to Link-State Approach Dijktra Algorithm: Finding hortet path in order Baic idea: two tep procedure Each ource node get a map of all node and link metric (link tate) of the entire network Find the hortet path on the map from the ource node to all detination node Broadcat of link-tate information Every node i in the network broadcat to every other node in the network: ID of it neighbor: i =et of neighbor of i Ditance to it neighbor: {C ij j i } Flooding i a popular method of broadcating packet Find hortet path from ource to all other detination w' w w" Cloet node to i hop away nd cloet node to i hop away from or w rd cloet node to i hop away from, w, or x x x' z z' Dijktra algorithm : et of node for which hortet path already found Initialization: (Start with ource node ) = {}, D =, i ditance zero from itelf D j =C j for all j, ditance of directly-connected neighbor Step A: (Find next cloet node i) Find i uch that D i = min Dj for j Add i to If contain all the node, top Step B: (update minimum cot) For each node j D j = min (D j, D i +C ij ) Go to Step A Minimum ditance from to j through node i in Execution of Dijktra algorithm Iteration D D D D D Initial {} {,} {,,} 7 {,,,} {,,,,} {,,,,,}

14 Shortet Path in Dijktra Algorithm Reaction to Failure If a link fail, Router et link ditance to infinity & flood the network with an update packet All router immediately update their link databae & recalculate their hortet path Recovery very quick But watch out for old update meage Add time tamp or equence # to each update meage Check whether each received update meage i new If new, add it to databae and broadcat If older, end update meage on arriving link Another Approach: Source Routing Example Source hot elect path that i to be followed by a packet Strict: equence of node in path inerted into header Looe: ubequence of node in path pecified Intermediate witche read next-hop addre and remove addre Source hot need link tate information or acce to a route erver Source routing allow the hot to control the path that it information travere in the network Potentially the mean for cutomer to elect what ervice provider they ue,,,b A Source hot,,b,b B B Detination hot Chapter 7 Packet-Switching etwork Overview of etwork Aynchronou Tranfer Mode () Packet multiplexing and witching Fixed-length packet: cell Connection-oriented Rich Quality of Service upport Conceived a end-to-end Supporting wide range of ervice Real time voice and video Circuit emulation for digital tranport Data traffic with bandwidth guarantee Detailed dicuion in Chapter 9

15 etworking TDM v. Packet Multiplexing Voice Video Packet Voice Video Packet Adaptation Layer etwork Adaptation Layer TDM Packet Variable bit rate Multirate only Eaily handled Delay Burt traffic Proceing Low, fixed Inefficient Minimal, very high peed Variable Efficient Header & packet * proceing required End-to-end information tranport uing cell -byte cell provide low delay and fine multiplexing granularity Support for many ervice through Adaptation Layer * In mid-98, packet proceing mainly in oftware and hence low; By late 99, very high peed packet proceing poible : Attribute of TDM & Packet Switching Switching Voice Data packet Image Packet tructure give flexibility & efficiency Synchronou lot tranmiion give high peed & denity TDM MUX Wated bandwidth Packet Header Switch carrie out table tranlation and routing video voice data video Switch voice 7 video 7 data 9 video 7 witche can be implemented uing hared memory, hared backplane, or elf-routing multi-tage fabric Virtual Connection Virtual connection etup acro network Connection identified by locally-defined tag Header contain virtual connection information: 8-bit Virtual Path Identifier -bit Virtual Channel Identifier Powerful traffic grooming capabilitie Multiple VC can be bundled within a VP Similar to tributarie with SOET, except variable bit rate poible Phyical link Virtual path Virtual channel VPI/VCI witching & multiplexing a b c d e Sw VPI VPI VPI Sw = witch croconnect VPI Sw Sw Connection a,b,c bundled into VP at witch Croconnect witche VP without looking at VCI VP unbundled at witch ; VC witching thereafter VPI/VCI tructure allow creation of virtual network a d e Sw b c